Knob and Tube Wiring in Older Waterloo Region Homes

If you own an older home in Galt, Hespeler or Preston, or in one of the older neighbourhoods of Kitchener or Waterloo, there may be knob and tube wiring somewhere behind your walls. It is not automatically dangerous, but it was designed for a very different household, and it can affect your insurance and your renovation plans. Here is what it is, how to recognise it without touching it, and what replacing it involves.

What knob and tube wiring is

The Electrical Safety Authority (ESA) describes knob and tube, more recently called open wiring, as a wiring method used in homes from the early 1900s to the 1940s. It is no longer installed today.

Instead of a modern cable, it uses separate insulated conductors. Where they pass through joists or studs, they run through ceramic tubes. Along the framing, they are tied to ceramic knobs that act as standoffs. That is where the name comes from.

The big difference from modern wiring is that there is no bonding conductor, the third wire that connects receptacles to ground. That is why homes with knob and tube usually have two-prong outlets. Our post on two-prong outlets and ungrounded circuits covers that side of the problem in detail.

How to spot it (look, don’t touch)

ESA’s podcast on the subject points to the unfinished basement as the easiest place to check: stand underneath and look up between the floor joists. Signs include:

• White ceramic tubes passing through the joists, with single wires running through them
• Ceramic knobs along the joists with wires tied to them, usually as two separate runs
• Wires with an old rubber, cloth-like covering rather than a modern plastic-sheathed cable
• Two-prong outlets in the rooms upstairs

A finished basement does not rule it out. ESA notes that many owners replaced the exposed runs in the basement but left knob and tube running up inside the walls, so it can take further investigation to find. Three-prong outlets are not proof either: ESA has seen newer cable spliced onto knob and tube with a bonding wire that connects to nothing.

Please only look. Don’t pull on, move or tape the wires, and don’t store things on the joists where they run, which ESA notes is often how the insulation gets damaged. Don’t dig through attic insulation to look for it either. Natural Resources Canada (NRCan) advises not to disturb vermiculite insulation, which may contain asbestos. If you are not sure what you are looking at, a licensed electrician can confirm it.

Why it is a concern today

ESA’s position is balanced. It says knob and tube is safe provided it is properly maintained by a Licensed Electrical Contractor (LEC), and it calls the idea that all of it must be disconnected and replaced a myth. The concerns come from age, past alterations and modern demand:

• No ground. There is no bonding conductor, and the original design has none of the modern protections ESA lists, such as GFCIs for wet locations, dedicated circuits and arc-fault protection.
• Ageing insulation. ESA notes the rubber, cloth-like insulation can become brittle over time, especially where it is exposed, at outlets and lights, and from heat and regular use.
• Buried in insulation. NRCan warns never to let insulation materials come into contact with old knob and tube wiring, because it can pose a fire hazard. This matters if you are planning to top up your attic insulation.
• Overloading. These homes were wired with very few circuits. ESA says they may not have the capacity for today’s needs, and it classifies some common workarounds as unsafe, including extension cords used as permanent wiring and 20 or 30 A fuses put in place of 15 A fuses.
• Amateur splices and add-ons. ESA also flags receptacles added to existing circuits and improper connections to knob and tube. That work should only be done by an LEC.

ESA’s guidance is that existing knob and tube can stay in place if it is protected by a 15 A fuse or breaker, no outlets have been added that overload the circuit, and the visible conductors look to be in good condition. It should be replaced where exposed conductors show damage or deterioration, poor connections, overheating, or alterations that result in overloading.

The insurance question

ESA says buyers and owners of older homes are finding that many insurers will not provide or renew coverage on homes with knob and tube, and some require a total replacement first. Requirements differ between companies, so before you buy or renew:

• Tell your own insurer or broker what wiring the house has
• Ask exactly what they need: an assessment, partial replacement or full removal
• Get their answer in writing so the scope of work matches what they will accept

After any rewiring, keep the ESA Certificate of Acceptance. ESA describes it as an important document for insurance purposes and resale.

What replacing it involves

1. An electrical assessment. ESA recommends having an LEC assess the home’s electrical system. This is different from a home inspection because it focuses only on the electrical: the visible wiring, what is on each circuit, the fuses or breakers protecting them, and any add-ons over the years.

2. A notification of work with ESA. ESA says homeowners planning to modify knob and tube should have the work done by an LEC, and a notification of work (the ESA permit) has to be filed. Your contractor files it and arranges the inspection. Our guide to ESA permits explains how that works.

3. New circuits built to today’s code. ESA’s bulletin on alterations in dwelling units says that when knob and tube is replaced to existing receptacle locations, the new receptacles must be grounded three-prong, tamper-resistant types, and the circuits need arc-fault (AFCI) protection. ESA also recommends adding outlets during a rewire, since the old ones are rarely where you need them and extension cords are not meant to be permanent.

4. Fishing cable, not gutting the house. ESA notes that a full gut is not usually needed. New cable is fished through small openings cut in specific spots, which is easier with an unfinished basement and harder in two and three storey homes. Visible knob and tube is cut out, and concealed runs are cut and pushed back so they cannot be reused.

5. Patching. The openings will need to be patched and painted, so ask whether that is included in your quote. ESA also points out that some older homes may contain asbestos, which is worth checking before any walls are opened.

6. Phased rewiring, where it makes sense. Some owners rewire in stages, for example the basement and exposed runs first, then floor by floor, as long as the remaining knob and tube still meets ESA’s conditions. Check with your insurer before choosing this route, since some require full replacement.

A rewire adds circuits, so it is also a good time to look at your panel. ESA notes that some insurers ask about the electrical service as well and may require an upgrade. See our 100 amp vs 200 amp panel upgrade guide for what that decision involves.

Get an honest assessment

If you are buying or renovating an older house in Cambridge or Kitchener-Waterloo, it pays to know what is behind the walls first. Knob and tube and ungrounded circuit rewiring is part of our residential electrical services. Borealis Electric is owned by a Master Electrician (ECRA/ESA licence #7017294), fully insured, with 15+ years of experience. Contact us for a free quote, or call (519) 240-5151.